FR2612916A1 - TREATMENT OF BOURBIER WATER RELEASE CONTAINING LIGNOSULFONATES - Google Patents

Abstract

Method for treating drilling effluents containing ligno-sulfonates wherein, successively, sulfuric acid is injected in order to cause a coagulation, a cationic polyelectrolyte is injected to cause a flocculation and solids are separated from the liquid by centrifugation or dewatering-compaction.

Description

 The present invention relates to a method for treating waste water discharges and a device for implementing said method. It applies more specifically to the treatment of water from quagmires for oil drilling.

 Drilling effluents are mainly composed of drilling mud diluted by washing water, they cannot be discharged into a river without treatment.

 The essential parameters governing the authorization of discharge are color, odor, chemical oxygen demand (COD), biological oxygen demand (BOD), suspended matter (MES), dissolved salts, content in hydrocarbons, finally toxicity.

 Ligno-sulfonates are used for the treatment of sludge as both a dispersant and an inhibitor of swelling of clays, a filtrate reducer and cake enhancers, resistant to high concentrations of calcium and NaCl and at high temperatures, they act on color which turns from brown to black and on the COD which increases significantly.

 The current treatment does not effectively remove lignosulfonates, because it is based on anionic flocculation coagulation in a single operation.

 The new process avoids this disadvantage by successively performing and separating coagulation and flocculation, which allows the control and development of each step.

 A method according to the invention, on a treatment line, comprises the following steps: injection of sulfuric acid to cause coagulation, then addition of a 100 t cationic polyelectrolyte to cause flocculation and finally separation of the solid phase by centrifugation or drainage-cornpactage.

 According to a preferred embodiment after the injection of sulfuric acid, on the one hand, the best coagulation is brought about while ensuring efficient mixing, preferably with a static mixer, and on the other hand, the most flocculation is caused. perfect by prolonging the contact between the 100% cationic polyelectrolyte and the effluent by circulating the mixture in a flocculation loop whose length and diameter are determined taking into account the flow rate and the quality of the sludge to be treated.

 In the same embodiments, a control of the PH is ensured before entering the injection device for 100% cationic polyelectrolyte. The PH is kept at a value lower than 6. A device for injecting fresh water at a point on the treatment line located before the coagulation device makes it possible to dilute the effluent -if necessary.

 The separation of the solid and liquid phases at the end of treatment can be carried out using a centrifuge, however it is preferable on construction sites to use a drip-compactor.

 The invention will be better understood in the following description, given without limitation, of a device, intended for the implementation of the proposed method, illustrated with the aid of the attached figures.

- Figure 1: Diagram of the installation.

- Figure 2: Drainer-compactor device.

In Figure I, there is shown, schematically, a treatment line for the mud basin
(1) to the discharge into an external drainage (2) such as a river for the water and a discharge for the solid pelletizable phase (11).

On this line, there are successively - a conduit (3) of fresh water inlet for dilution
optional, - a device (4) for injecting dilute sulfuric acid
as required, - a static mixer (S), hflicoidal, coaxial device
of the duct, causing local increase in speed and
turbulence favorable to mixing - a device (6) for controlling the PH, - a device (7) for injecting polyelectrolyte, - a mixing device (8), - a device <9) called a flocculation loop, constituted by
a long tube, at least 25 bolsters placed
serpentine shape to reduce space and
promote contact, - finally a device (10) for solid liquid separation with
separate outlets for water drainage (2) and
the solid or rather muddy phase (11). The device (10)
can be constituted by a centrifuge. I1 can also
be constituted by a drip-compactor as it is
shown in Figure II.

 FIG. 11 represents a drainer-compactor comprising two parts: a grid (12) inclined at least 450 on the vertical on which the flocculated effluent slides separating into free water which passes through and goes to the discharge (2) and flocculated elements (13), and a compacting screw (14) towards which slide by gravity said flocculated elements (13) and which delivers at its end (15) a pelletizable effluent (11) while water passes through a grid of bottom (16) to also be oriented towards rejection (2).

Example of device operation
The treated sludge is bentonite with lignosulfonates with a density of = 1.04 to 1.05 and a treatment rate of 3 m3 / hour.

The treatment of such sludge with 0.75 kg of polyelectrolyte per m3 results in the changes in characteristics indicated below - the COD goes from 3.240 to 1.000-1.300, - the MES in mgr / liter from 40.000 to 200- 700, - the lignosulfonates in g / liter from 2.80 to 1-1.4, - the PH remains stable between 5 and 6, - the chlorides remain stable at 1.07 while they
grow with the anionic treatment, - the brown-black color tre becomes pale straw yellow.

 Add that acidification with SO4H2 is less expensive than with HCl and eliminates an appreciable fraction of Ca ++ ions, which makes the residual water more usable for making fresh mud.

Claims (10)

1 - Process for treating effluents with water content  significant in particular drilling effluents containing  lignosulfonates, characterized in that  successively, on a treatment line, we inject  sulfuric acid to cause coagulation, we  then injects a 100 t cationic polyelectrolyte of  so as to cause flocculation and finally we centrifuge  to cause separation into liquid phases and  solid. 2 - Method according to claim 1 wherein, after  have injected sulfuric acid and caused the best  mixture of this sulfuric acid with the effluent, we  controls the average PH of said effluent and we add this  which is necessary to keep this PH below 6. 3 - Method according to claim 1 wherein after having  injected a cationic polyelectrolyte 100 8, we cause  the best mixture and we maintain contact between  said polyelectrolyte and effluent for a time  long enough for flocculation to be effective  before performing centrifugation. 4 - Device for treating effluents with water content  significant, in particular drilling effluents containing  lignosulfonates, comprising successively, on a  processing line, means  - sulfuric acid injection,  - mixing this sulfuric acid with the effluent,  - control of the PH and its maintenance such as PH  less than 6,  - injection of a 100% cationic polyelectrolyte,  - mixing said polyelectrolyte with the effluent,  - maintaining the polyelectrolyte in the presence of  the effluent by the use of a loop of  flocculation of sufficient length underground in  function of the flow, and finally,  - separation of the solid and liquid phases. 5 - Device according to claim 4 wherein the  means for mixing sulfuric acid and effluent  consist of a static mixer. 6 - Device according to claim 4, wherein the  means of separation of the solid and liquid phases are  constituted by a centrifuge. 7 - Device according to claim 4, wherein the  means of separation of the solid and liquid phases are  consisting of a compacting drip tray. 8 - Device according to claim 4 wherein the Ph  before the polyelectrolyte injection is maintained the  as close as possible to 5.5. 9 - Device according to claim 4 wherein the  polyelectrolyte and effluent are mixed  with a fixed helical ramp, coaxial with the line of  treatment. 10- Device according to claim 4 wherein the  flocculation loop has a length of at least twenty  five meters.